Microwave treating device



Sept. 17, 1968 P- c. MULLER MICROWAVE TREATING DEVICE 2 Sheets-Sheet l Filed Oct.

INVENTOR" 104 Cum-11701451? W424. 20TH ATTORNEY p 7, 1968 P. c. MULLER 3,402,277

MI CROWAVE TREAT ING DEVI CE Filed Oct. 6, 1966 2 Sheets-Sheet 2 TIEILJ.

INVENTOR /Q4u4 Over/W041i? BY rmzz. e/m/ ATTORNEY United States Patent 3,402,277 MICROWAVE TREATING DEVICE Paul Curt Miiller, Wettingen, Switzerland, assignor to Patelhold Patentverwertungs- & Elektro-Holding A.G., Glarus, Switzerland Filed Oct. 6, 1966, Ser. No. 584,913 Claims priority, application Switzerland, Oct. 25, 1965, 14,697/65 6 Claims. (Cl. 21910.55)

The invention relates to a micro-wave treatment tunnel wherein the goods to be treated, for example pulverulent or granular material or piece goods, are passed through the heating zone with the aid of a conveyor belt.

There are known microwave treatment tunnels wherein a hollow guide of substantially rectangular cross-section, through which the goods being treated are passed, is fed with microwave energy, with the result that hollow-guide Waves are excited in a definite mode or at most in one of a few modes. Such a treatment tunnel has the disadvantage that the load .which it presents to the microwaves fed into it depends to a very marked extent on the type and dimen sions of the goods introduced for treatment.

As a result of this, the conditions for maintaining stable operation are very critical. A further disadvantage resides in that a plurality of generators cannot be operated in parallel on account of the difliculty of decoupling by simple means.

The object of the invention is to provide a microwave treatment tunnel wherein these disadvantages are to a large extent avoided.

The microwave treatment tunnel according to the invention is characterized in that the planes which bound it are arranged in pairs at a distance from one another of at least double the length of the microwaves in free space, in that the tunnel member comprises four further oblique internal bounding planes which are not parallel to one another, each linking one horizontal and one vertical bounding plane and being at an include-d angle of 20- 70 to the vertical, and in that the microwave feed takes place across a plurality of cross sections of the tunnel member, in such a way that the mean direction of the density of energy flow fed in is diflerent at least for neighbouring feed cross-sections.

The invention will be explained by way of example with reference to the drawing in which:

FIG. 1 is a cross-sectional view of one form of device made according to the invention.

FIG. 2 is a cross-sectional view, similar to FIG. 1 but shown without the conveyor belt, of another form of device rnade according to the invention.

FIG. 3 is a plan view of the device of FIG. 2.

FIG. 1 Sil'lOWS a section through a first variant. The tubular tunnel member 1 is of octagonal cross-section. A conveyor belt, of which the forward and return runs 3 and 4 respectively are supported by freely rotatable nonmetallic rollers 5, 6, serves to convey the goods 2 being treated through the tunnel. Feed takes place across four different cross-sections of the tunnel via hollow guides 7 10 which are flanged on to the tunnel member 1. Each of the hollow guides receives microwave energy from an associated microwave generator (not shown) via an input coupling 11, for example, for the purpose of forming an H wave, and delivers it through a feed aperture, for example 12, into the treatment tunnel. Teflon plates 12' are clamped between the flanges of the hollow guides and the tunnel member 1 in order to prevent the hollow guides from becoming dirty. The cross-sectional dimensions of the tunnel are so chosen that the microwaves fed in are propagated in a manner similar to that in free space. This is achieved as a result of the fact that its horizontal and vertical dimensions are at least double the length of the microwaves in free space (A). The oblique bounding planes which are not parallel to one another produce a large number of reflections, with the result that the field of radiation is to a large extent isotropic.

In order to distribute as uniformly as possible the action of the energy radiated from the feed apertures directly onto the goods being treated, the four feed apertures are arranged offset along a spiral across four different oblique planes bounding the tunnel. The mean direction of the density of energy flow fed in is thus diiferent for two neighbouring (feeds.

The freely rotatable rollers 5, 6 are mounted in the vertical walls of the tunnel member. In order to prevent the space beneath the conveyor belt from becoming greater than is necessary, the lower oblique bounding planes are less steep than the upper ones as indicated by the angle or exceeding the angle 5 in the drawing. In other Words, in the example according to FIG. 1 the two pairs of opposite walls 1a, 1b and 1c, 1d of the tunnel 1 are parallel to one another, while the pairs of opposite :walls 1g, 111 and 1e, 1 form acute angles with one another.

The variant in FIGURE 1 has the advantage of being particularly simple in construction. In this case, the directions of oscillation are all substantially parallel to the cross-sectional planes, as shown by arrows a in FIGURE 1. It has been found that sufficiently good decoupling is attained with this variant in most cases.

In order still further to improve the decoupling, the hollow guides may be so arranged that the included angles between the electric field strengths and the cross-sectional planes are different for two neighbouring feeds.

In a further variant shown in FIGURES 2 and 3, the electric field strengths for the feed cross-sections are alternately parallel and perpendicular to the cross-sectional planes. FIGURES 2 and 3 show the tunnel member 1 with flanged'on hollow guides 13-16 in section and plan. The feed apertures are arranged in the horizontal and vertical planes bounding the tunnel member. The hollow guides 13 and 15 are bent obliquely to one side in order to provide favourable accommodation for the generators.

The improvement in decoupling may be carried still further. For this purpose, the feed apertures are provided with polarising grids which are clamped together with the Teflon cover plates between the flanges of the hollow guides and the tunnel member.

When relatively large piece goods are being irradiated, it may happen that a relatively high percentage of the microwave energy radiated from one feed aperture directly on to the goods being treated will be reflected back into the hollow guide, which will lead to a widely fluctuating load on the generator on account of the movement of the piece goods. In order to avoid this, a transformation plate 17, for example, may be fitted inside the tunnel in front of each of one or more feed apertures. These transformation plates, which are at a distance of less than 4 from the wall of the tunnel, cause the microwave energy to enter the tunnel substantially at a tangent.

In the foregoing the invention has been described in reference to a few illustrative devices or systems. It will be evident, however, that variations and modifications, as well as the substitution of equivalent devices or elements for those shown and described herein for illustration, may be made in accordance with the broader purview and spirit of the invention as set forth in the appended claims. The specification and drawings are accordingly to be regarded in an illustrative rather than in a restrictive sense.

I claim:

1. Microwave treatment tunnel with an endless conveyor belt which is guided through an electrically conductive tunnel member having two horizontal and two 3 vertical inner bounding planes, characterized in that these bounding planes are arranged in pairs at a distance from one another of at least double the length of the microwaves in free space, in that the tunnel member (1) comprises four further oblique internal bounding planes which are not parallel to one another, each linking one horizontal and one vertical bounding plane and being at an included angle of 20-70 to the vertical, and in that the microwave feed takes place across a plurality of crosssections of the tunnel member, in such a way that the mean direction of the density of energy flow fed in is different at least for neighbouring feed cross-sections.

2. Microwave treatment tunnel according to claim 1, characterized in that the return run of the conveyor belt (4) takes place inside the tunnel member, and in that the conveyor belt (3, 4) is supported by a plurality of freely rotatable non-metallic rollers (5, 6) arranged in two horizontal planes and extending transversely across the tunnel.

3. Microwave treatment tunnel according to claim 1, characterized in that for each feed there is a microwave generator from which the microwave energy is passed via a hollow guide to a feed aperture in the tunnel member.

4. Microwave treatment tunnel according liO claim 3, characterized in that the feed apertures for neighbouring feed crosssections are arranged in two different oblique internal planes bounding the tunnel member.

- 5. Microwave treatment tunnel according to claim 3, characterized in that for the flow of energy fed in the in cluded angles between the electric field strengths and the cross-sectional planes are dilferent for two neighbouring feeds.

6. Microwave treatment tunnel according to claim 5, characterized in that at least one feed aperture is provided with a polarising grid.

References Cited UNITED STATES PATENTS 2,814,708 11/1957 B lass 2 1910.55 3,196,242 7/1965 De Vries et al. 21910.55-

FOREIGN PATENTS 426,051 12/1966 Switzerland.

RICHARD M. WOOD, Primary Examiner.

L. H. BENDER, Assistant Examiner. 

1. MICROWAVE TREATMENT TUNNEL WITH AN ENDLESS CONVEYOR BELT WHICH IS GUIDED THROUGH AN ELECTRICAL CONDUCTIVE TUNNEL MEMBER HAVING TWO HORIZONTAL AND TWO VERTICAL INNER BOUNDING PLANES, CHARACTERIZED IN THAT THESE BOUNDING PLANES ARE ARRANGED IN PAIRS AT A DISTANCE FROM ONE ANOTHER OF AT LEAST DOUBLE THE LENGTH OF THE MICROWAVE IN FREE SPACE, IN THAT THE TUNNEL MEMBER (1) COMPRISES FOUR FURTHER OBLIQUE INTERNAL BOUNDING PLANES WHICH ARE NOT PARALLEL TO ONE ANOTHER, EACH LINKING AT AN INZONTAL AND ONE VERTICAL BOUNDING PLANE AND BEING AT AN INCLUDED ANGLE OF 20-70* TO THE VERTICAL, AND IN THAT THE MICROWAVE FEED TAKES PLACE ACROSS A PLURALITY OF CROSSSECTIONS OF THE TUNNEL MEMBER, IN SUCH A WAY THAT THE MEAN DIRECTION OF THE DENSITY OF ENERGY FLOW FED IN IS DIFFERENT AT LEAST FOR NEIGHBOURING FEED CROSS-SECTIONS. 